# include <bits/stdc++.h>
# define INF 0x7fffffff
# define MAXN 
using namespace std;

inline char getc(){
    static char buf[1 << 18], *fs, *ft;
    return (fs == ft && (ft = (fs = buf) + fread(buf, 1, 1 << 18, stdin)), fs == ft) ? EOF : *fs++;
}

inline int gn() {
    int k = 0, f = 1;
    char c = getc();
    for(; !isdigit(c); c = getc()) if(c == '-') f = -1;
    for(; isdigit(c); c = getc()) k = k * 10 + c - '0';
    return k * f;
}

int c, v0, v1, a, l, day, fsh, dr;

int main() { 
# ifdef LOCAL
    freopen("in", "r", stdin);
# endif
    c = gn(), v0 = gn(), v1 = gn(), a = gn(), l = gn();
    day = 0;
    dr = v0;
    while(fsh < c) { 
        fsh += dr - ((fsh) ? l : 0);
        dr += a;
        dr = min(dr, v1);
        day++;
    }
    printf("%d\n", day);
    return 0;
}
